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Investigation of Wicking Geotextile for Moisture Reduction and Interaction of Soil with Fines
Zaman, Md. Wasif
Zaman, Md. Wasif
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Abstract
Geotextiles, made of synthetic materials like polyester and polypropylene, have long been used for drainage in pavements. However, they are often ineffective to remove moisture under unsaturated soil conditions after precipitation and/or groundwater rise, leading to pavement distresses. To address these problems, a wicking geotextile with specialized nylon fibers, featuring deep grooves for high capillary forces, has been developed. This geotextile efficiently absorbs and removes water from its surrounding soil, mitigating pavement distresses resulting from frost heave, freeze-thaw, and poor drainage.
To drain water out of road sections, the geotextiles need to get wet first. In this study, the wettability of three different types of geotextiles, namely wicking woven (WW) geotextile, non-wicking woven (NWW) geotextile, and nonwoven (NW) geotextile, was investigated in terms of their contact angles dependent on water-geotextile interaction. Test results show that the contact angle decreased to smaller than 90° and the droplet disappeared on the wicking woven geotextile within a few seconds after water dropping, while the contact angle remained larger than or approximately equal to 90° on the other two types of geotextiles within the observation period. This comparison indicates that water penetrated faster into the wicking woven geotextile than other geotextiles.
Subgrade soils and base courses under pavements often remain unsaturated throughout their service life, except during precipitation or changes in groundwater levels. The content of moisture present in a soil under an unsaturated condition after gravitational drainage is termed as the field moisture capacity (FMC), commonly used by soil scientists and agricultural engineers to assess water availability for plants. However, laboratory methods to determine FMC are lacking. Hence, a simple test method was developed in this study to determine FMCs for sands at different fines contents (0%, 5%, 10%, and 15%).
The effectiveness of the wicking geotextile in reducing soil moisture is influenced by fines in the soil. The limit for the effectiveness of the wicking geotextile in unsaturated soils at fines contents remains unknown. This study developed a simple moisture reduction test method using polycarbonate test boxes as soil columns in the laboratory to quantify the effectiveness of the wicking geotextile in reducing moisture in sands at different fine contents (0%, 5%, 10%, and 15%) and waiting periods (3, 7, 14, and 28 days). A non-wicking woven geotextile was used for comparison. Test results reveal that the moisture reduction by the wicking geotextile decreased with the fines content in the silty sand, while the non-wicking geotextile hindered water flow, leading to moisture accumulation. The measured moisture content profile in the soil column indicated the influence zone of the wicking geotextile varied with the fines content.
Woven geotextiles are commonly employed to reinforce slopes, walls, and roads, where soil-geotextile interface shear strength is an important design parameter. While the wicking geotextile can enhance hydraulic performance in such applications, the interface behavior and properties of the wicking geotextile with its surrounding soils are not well investigated. This study conducted large interface shear tests to assess wicking geotextile-sand interface strengths, considering a range of fines and moisture contents. The calculated interaction coefficients between the wicking geotextile and sands with 0%, 5%, and 10% fines were 0.9, 0.81, and 0.78, respectively, under normal stresses of 12.5, 25.0, and 50.0 kPa.
Moisture adversely affects road performance by softening subgrade soil, reducing load-bearing capacity, and increasing compressibility. Previous studies mostly focused on the improvement of aggregate bases by the wicking geotextile under rainfall conditions. However, little is known about the benefits of the wicking geotextile in improving sandy subgrade with fines, especially at field moisture capacities under cyclic loading. Six large-scale cyclic plate loading tests were conducted to investigate control, wicking-geotextile improved, and non-wicking geotextile improved sections on sand subgrades with 0% and 10% fines. A 10-day drainage period was allowed for all test sections. Test results show the wicking geotextile reduced moisture from both aggregate base and sand subgrade at a field moisture capacity condition and permanent deformations of the aggregate base over the sand subgrades with 0% and 10% fines due to the combined mechanical stabilization and drainage effects.
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Date
2024-01-01
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University of Kansas
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Keywords
Civil engineering, Geotechnology, Field moisture capacity, Interaction coefficient, Moisture reduction, Permanent surface deformation, Silty sand, Wicking geotextile